fixed bug the recording of the drscheme:htdp:last-set-teachpacks preference
fixed bug the recording of the drscheme:htdp:last-set-teachpacks preference

svn: r7012

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket